This invention relates to glycidyl esters whose adducts with acrylic or methacrylic acid exhibit increased effective glass transition temperatures and their use as reactants in preparing polymer compositions.
1. Description of Related Art
Glycidyl esters of monocarboxylic acids are well known materials which are useful as chemical intermediates in the preparation of acrylic, polyester, and alkyd resins, or as reactive diluents in the preparation of thermoset epoxy, polyester and urethane paints and coatings.
Of particular interest are glycidyl esters of aliphatic monocarboxylic acids represented by the empirical formula 
wherein R1, R2 and R3 each represent the same or different alkyl radicals of normal or branched structure containing 1-20 carbon atoms, and R4 through R8 each represent hydrogen or a hydrocarbyl group containing 1-3 carbon atoms. A more preferred product is one where R1 through R3 are alkyl radicals containing a sum total of 3-20 carbon atoms and where R4 through R8 are each hydrogen, e.g., the reaction product of neodecanoic acid (R1+R2+R3=C8) and epichlorohydrin.
Glycidyl esters of this general type and their method of preparation are disclosed in U.S. Pat. No. 3075999, U.S. Pat. No. 3178454, U.S. Pat. No. 3275583 and U.S. Pat. No. 3397176, the complete disclosures of each of which are incorporated herein by reference.
Such glycidyl esters can be made by reacting an alkali salt of the carboxylic acid with a halo-substituted monoepoxide such as an epihalohydrin, e.g., epichlorohydrin (1-20 molar excess). The mixture is heated (50xc2x0-150xc2x0 C.) in the presence of a catalyst forming glycidyl ester plus alkali salt and water. The water and excess epihalohydrin are removed by azeotropic distillation, and the salt by-product, e.g., NaCl, is removed by filtration and/or washing. The glycidyl esters can also be made by reacting the carboxylic acid directly with epichlorohydrin under similar process conditions. The chlorohydrin ester intermediate formed during this reaction is subsequently treated with an alkaline material, e.g., sodium or potassium hydroxide, which yields the desired glycidyl ester. By-product salt is removed by washing and/or filtration, and water is removed by drying.
Investigations of these reactions reveal that several heavier by-products are produced during the reactions to varying degrees, and species which add color to the main product are contained within the heavier by-products. The heavier by-products include the reaction products of the glycidyl ester product and/or the chlorohydrin ester intermediate with either unreacted epichlorohydrin, unreacted monocarboxylic acid or salt and/or water at various stages of the synthesis process in accordance with the following overall reaction schemes: 
The heavier by-products may also include further reaction products of compounds A, B and/or C with the glycidyl ester product and other species present. Generally speaking, one or a combination of these or other unidentified heavies are present in the glycidyl ester reaction product at levels in excess of about 3 wt %, e.g., about 4-12 wt %.
Because glycidyl esters are thermally and chemically reactive molecules, separation of these by-products from glycidyl esters is not easily accomplished. Standard atmospheric distillation techniques have been found to increase the amount of by-products as well as the degree of color of the esters. It is believed that this increase in color is caused by the reaction at elevated temperatures, as encountered during distillation, of the glycidyl functionality present in the desired product with functionalities present in the by-products, thereby forming additional by-products. Surprisingly, standard vacuum distillation has also been found to be ineffective in reducing the initial or aged color of the glycidyl esters, and tends to worsen the color problem.
Japanese Patent 46 (1971) 37326 discloses a process for manufacturing an unsaturated organic acid glycidyl ester by reacting a salt of the unsaturated acid (acrylic or methacrylic acid) with a molar excess of epichlorohydrin. The residual unreacted epichlorohydrin is then distilled out of the reaction product using thin film distillation techniques. The resulting product is further distilled using thin film evaporation techniques to provide a purer product having improved color stability after periods of storage. The reference teaches that the process avoids the polymerization of the acrylic monomers observed during conventional distillation and thereby eliminates the need to include a polymerization inhibitor in the reaction product which inhibitor retards polymerization of the unsaturated monomers but which also reacts with the epoxy compounds to give products of less purity.
Copending U.S. application Ser. No. 08/861,408, filed May 21, 1997, discloses a process for the distillation of the glycidyl ester reaction product composition of one or more straight or branched chain saturated monocarboxylic acids or salts thereof and a halo-substituted monoepoxide comprising subjecting said reaction product composition to conditions of temperature and vacuum in a thin film, short pass distillation apparatus, and recovering a light fraction having a Ptxe2x80x94Co color value of less than about 100 after 20 days storage in contact with air at about 125xc2x0 C., as measured in Ptxe2x80x94Co units in accordance with ASTM D1209.
Products produced according to that invention are of significantly reduced initial color and exhibit improved color stability after periods of storage, thereby minimizing any color contribution by these products in systems where they are used, e.g., in the preparation of alkyd, polyester or acrylic resins and especially in coating and paint formulations containing these products.
Various researchers have been pursuing new polymer compositions which will give a better balance of properties when these polymeric binders are formulated into paints. Of particular importance is maintaining good film properties (hardness, flexibility, durability, etc.) as polymer molecular weights and viscosity are reduced. The latter is essential to reduce the amount of solvent, i.e., volatile organic compounds (VOCs), in the paints. These VOCs are being regulated to reduce air pollution.
One important factor which influences paint and film properties is the glass transition temperature (Tg) of the polymer(s) and/or oligomer(s) used as paint binders. Usually a specific value or range of Tg is required to meet the performance requirements of a given application. Another important factor which influences paint and film properties is the nature of the functional group incorporated in the polymer. In many cases this is a hydroxyl group. One of the better hydroxyl groups used in acrylic polymers, for example, comes from an adduct of glycidyl neodecanoate and either methacrylic acid or acrylic acid. These adducts can impart improved paint and film properties over similar acrylic polymers (same OH concentration, Tg, and molecular weight) made with other hydroxy functional monomers. Improved weatherability and chemical resistances and lower viscosity (i.e., lower VOC) are notable features attributable to these adducts.
It is a significant challenge, however, to obtain useful lower molecular weight acrylic polymers with hydroxy (OH) functionalities based solely on these adducts. In particular, as molecular weights decrease, one must increase the relative proportion of hydroxy functional monomers to maintain good film properties. With glycidyl neodecanoate adducts which have relatively low effective Tgs, this can lower the maximum polymer Tg below desired levels. Consequently, to get the best possible film properties one would like to have a monomer which provides the durability and chemical resistance of the glycidyl neodecanoate adducts, but with a higher Tg.
We have discovered that by using purified glycidyl esters of neo acids particularly those derived from isobutylene and/or isobutylene oligomers, one can obtain glycidyl ester adducts with high effective Tgs. Such glycidyl neopentanoate, glycidyl neononanoate, etc., adducts offer the possibility to make improved resin binders with desired Tgs, lower molecular weights (lower VOC) and superior film properties.
The present invention provides a glycidyl ester product having the formula: 
wherein R1, R2 and R3 each represent the same or different alkyl radicals of normal or branched structure containing 1-20 carbon atoms and R4 through R8 each represent hydrogen or a hydrocarbyl group containing 1-3 carbon atoms, and wherein said ester product is recovered as a light fraction from a glycidyl ester reaction product composition that has been subjected to conditions of temperature and vacuum in a thin film, short pass distillation evaporator, said purified glycidyl ester product further characterized that its polymerizable reaction product with methacrylic acid has a higher effective glass transition temperature as compared with the polymerizable reaction product with methacrylic acid of said glycidyl ester reaction product composition prior to purification.
The invention also provides for coating and paint formulations containing the purified glycidyl ester product as a reactive diluent or as a component useful in the preparation of resinous binder materials such as alkyd, polyester or acrylic resins.
Glycidyl ester products which are distilled in accordance with this invention are of the general structure set forth in formula 1 in the Background section of this disclosure, and which are the reaction product of one or a mixture of saturated monocarboxylic acids, preferably the alkali or tertiary ammonium salts thereof, and a halo-substituted monoepoxide.
Suitable saturated monocarboxylic acids which may be used to prepare the glycidyl esters are tertiary alkyl acids wherein R1, R2, and R3 in formula 1 above each contain 1-20 carbon atoms, more preferably 1-12 carbon atoms. More preferably, the sum total of R1, R2 and R3 is 3 to 15 carbon atoms and most preferably about 8 carbon atoms. Suitable such acids include neopentanoic (pivalic), neodecanoic, neotridecanoic and neononanoic acids. A particularly preferred acid is a neodecanoic acid prepared by the reaction of mono olefins averaging 8-10 carbon atoms in the molecule with carbon monoxide and water in the presence of a suitable acidic catalyst.
The most preferred saturated monocarboxylic acids are those where the segment: 
has a neo section of isobutyl or an isobutyl oligomer such as diisobutyl.
Suitable halo-substituted monoepoxides which may be used to prepare the glycidyl esters include epichlorohydrin, 1-chloro-2,3-epoxyhexane, 1-chloro-2,3-epoxy-4-butyloctane, 1-chloro-2,3-epoxy heptane, 3-chloro-4,5-epoxydodecane, 3-chloro-4,5epoxynonane, 1-chloro-2,3-epoxy-4-cyclohexyloctane and like materials.
Glycidyl esters of this type and their method of synthesis are well known in the art and are particularly described in the aforementioned U.S. Pat. No. 3178454 and U.S. Pat. No. 3075999. Isobutylene and diisobutylene are suitable starting monomers to prepare neo acids suitable for synthesis of the glycidyl esters of the invention.
A thin film, short pass distillation evaporator is used to separate the main glycidyl ester reaction product from by-products of the A, B and/or C type as described in the Background section of this disclosure, as well as other xe2x80x9cheaviesxe2x80x9d which may be present as impurities in the glycidyl ester reaction product. The term xe2x80x9cheaviesxe2x80x9d as used herein means compounds or mixtures of compounds having a molecular weight higher than the target glycidyl esters. The use of such evaporators allows for rapid vacuum stripping of the glycidyl ester from the mixed reaction product without subjecting the product to excessively high temperatures or for periods of time sufficient to cause thermal degradation of the product and the further development of one or more of the heavier by-products which tend to cause coloration of the product. Typical such evaporators include shell and tube evaporators, falling or rising film evaporators and wiped film evaporators. A preferred evaporator for use in preparing the purified products of the present invention is a wiped film evaporator.
The wiped film evaporators (also referred to as agitated thin-film evaporators) preferred for use in the distillation process are known in the art and are available commercially. A general discussion of the principle of operation of these evaporators may be found in the publication: xe2x80x9cAgitated Thin-Film Evaporators: A Three Part Reportxe2x80x9d, Parts 1 to 3; A. B. Mutzenburg, N. Parker and R. Fischer; Chemical Engineering, Sep. 13, 1965.
Typically, wiped film evaporators comprise a cylindrical evaporating vessel. The vessel may be either vertical or horizontal, with vertically arranged vessels being preferred. The evaporator further comprises a rotor mounted within the cylindrical evaporating vessel and provided with a number of wiper blades or wiper rollers, and a motor is provided to drive the rotor. The rotor is arranged within the cylindrical evaporating vessel so that, upon rotation by the motor, the wipers are caused to move over the inner surface of the cylindrical vessel. The wipers may contact the inner surface of the cylindrical vessel or, alternatively, a small gap or clearance may be left between the tips of the wiper blades or the tangential line of the wiper rollers and the inner surface of the cylindrical vessel.
In operation, the mixture to be separated is fed, supplied or subjected to the evaporator and forms a thin film over the inner surface of the cylindrical vessel. The film is heated, typically by means of indirect heat exchange with a heating medium through the wall of the cylindrical vessel, such as steam or hot oil. The action of the wiper blades in passing over the surface is to agitate the film of the glycidyl ester composition which forms on the inner cylinder surface, resulting in turbulence in the film, which in turn improves heat and mass transfer. In addition, the wiper blades or wiper rollers insure an even distribution of the composition over the inner surface of the vessel and prevent channeling of the liquid as it passes across the surface. Under the action of the wiper blades or wiper rollers and the heating, the lighter components of the mixture are caused to evaporate.
The light product is removed from the evaporator as a vapor and is subsequently condensed. Condensing is conveniently effected by indirect heat exchange with a cooling medium such as water. The condenser may be separate from the evaporator vessel or may be located within the vessel. In the latter case, the vessel will comprise a first evaporating section in which the rotor and wiper blades are arranged and a second condensing section in which the condenser is housed. If desired, a separating section may be disposed between the evaporating section and the condensing section to allow removal of any liquid droplets entrained in the vapor prior to condensing.
The heavy product is removed from the evaporator as a liquid flowing from the inner surface of the cylindrical vessel. The wiped film evaporator is operated under a vacuum. Suitable pumps for the generation and maintenance of the vacuum are well known in the art. Typical examples of suitable pumps include steam ejector pumps and diffusion vacuum pumps.
According to the process, the mixture to be separated is first heated to a temperature sufficient to reduce the viscosity of the mixture, thereby allowing it to more readily flow. The mixture is then introduced into the evaporator to form a thin film on the inner surface of the heat exchanger surface of the evaporator vessel, e.g., a cylindrical drum or a series of tubes. The operating pressures for the thin film evaporator will vary according to the precise nature of the ester feedstock. Typical operating pressures are in the range of about 0.05 to about 50 mm Hg, more preferably from about 0.5 to about 10 mm Hg. Typical operating temperatures in the evaporator will be in the range of from about 50xc2x0 C. to about 200xc2x0 C., more preferably from about 60xc2x0 C. to 175xc2x0 C. The average residence time of the glycidyl ester reaction product composition in the evaporator is relatively low as compared with that of a conventional batch distillation apparatus, and this is believed to be a key factor in the avoidance of discoloration of the distillate. Typical average residence time is in the range of from about 0.2 to about 10 minutes, more preferably less than about 2 minutes, depending upon the nature of the feedstock and the design of evaporator being employed. It is important, however, that the operating temperature is not so high as to lead to a substantial degree of thermal degradation of the mixture being processed at the particular residence time and that the operating conditions of temperature and pressure are selected to ensure that such high temperatures are not required.
Suitable wiped film evaporators which may be used in accordance with this invention include apparati of the type disclosed in U.S. Pat. No. 3878029, U.S. Pat. No. 4160692 or U.S. Pat. No. 4173246.
Preferred glycidyl esters purified in accordance with this invention will generally exhibit boiling points in the range of from about 60 to 90xc2x0 C. at 3mm Hg and a content of by-products such as A, B and/or C described in the Background section of this disclosure of less than 4 wt %, more preferably less than 2 wt % and most preferably less than 0.5 wt %. Coloration of the distilled product is in many cases reduced at least 50%, more preferably at least 60%, compared with the product coloration prior to distillation, as measured using the Ptxe2x80x94Co scale in accordance with ASTM test method D 1209. Glycidyl esters purified in accordance with this invention generally exhibit initial Ptxe2x80x94Co color values of less than 40 units prior to heat storage, more preferably in the range of 5-30 Ptxe2x80x94Co units, and values of less than about 100 Ptxe2x80x94Co units after 20 days storage in air at about 125xc2x0 C., or values of less than about 50 Ptxe2x80x94Co units after 20 days storage under an inert gas such as nitrogen at about 125xc2x0 C. These products also exhibit an at least about 3% reduction in epoxy equivalent weight (EEW) as compared with the non-purified starting material, more preferably a 4 to 8% reduction in EEW.
It has also been found that the purified glycidyl esters produced in accordance with this invention provide polymer compositions with a higher glass transition temperature (Tg) when used as a reactive diluent or monomer in the preparation of the polymer composition. For example, the polymerizable reaction product (ester) of the purified glycidyl ester with acrylic or methacrylic acid (which forms a hydroxy functional (meth)acrylate monomer) exhibits a higher effective Tg than the corresponding reaction product made using the non-purified glycidyl ester or an ester purified by other processes such as atmospheric distillation. Reaction products of preferred glycidyl ester materials with methacrylic acid will exhibit an effective Tg in the range of about 20xc2x0 C. to 90xc2x0 C., more preferably from about 20xc2x0 C. to 50xc2x0 C.
The glass transition temperature is related to the softening point of material and can be measured via a variety of techniques as discussed in Introduction to Polymer Science and Technology: An SPE Textbook, by H. S. Kaufman and J. Falcetta, John Wiley and Sons, 1977, and Polymer Handbook by J. Brandup and E. H. Immergut, editors, John Wiley and Sons, 1989. Tg values for high molecular weight homopolymers of various monomers are also available in these references. Values for copolymers can be calculated via the Fox Equation (Fox T. G., Bull Am. Phys. Soc. 1:123 (1956), i.e.             1      TG        =          ∑                        W          i                          Tg          i                      ,
where Wi is the weight fraction of the i th monomer in the copolymer, Tg,i is the glass transition temperature for a high molecular weight homopolymer of the i th monomer; and all temperatures are expressed in absolute units. Alternatively, if Tgs are known for all but one of the monomers and weight fractions are known for all monomers, a measurement of the Tg of the copolymer provides sufficient information to calculate an effective Tg for the last monomer. The latter procedure is used to calculate effective Tgs for the various glycidyl ester-methacrylic acid adducts used as monomers in Examples 8-12 of this application.
Since the number average molecular weights of the copolymers synthesized in Examples 8-12 (about 2000) is somewhat lower than values typically used with the Fox equation (more than about 10,000), the calculated Tg values for the adducts may be lower than their expected values. In particular, Tg values for high molecular weight polymers are generally independent of specific molecular weight, but Tg values for lower molecular weight polymers (less than about 10,000) often decrease as molecular weights decrease.
The purified glycidyl esters may be used in the preparation of acrylic resins which contain at least one hydroxy functional alkyl (meth) acrylate. This monomer will form by the reaction, under polymerization conditions, of the purified glycidyl ester and acrylic or methacrylic acid. In general, acrylic polymer resins may be prepared from at least one hydroxy functional alkyl (meth)acrylate, including the adduct described above, and at least one non-hydroxy substituted alkyl (meth)acrylate. Additional hydroxy-substituted alkyl (meth) acrylates which can be employed as monomers comprise members selected from the group consisting of the following esters of acrylic or methacrylic acid and aliphatic glycols: 2-hydroxyethyl acrylate, 3-chloro-2-hydroxypropyl acrylate, 1-hydroxy- 2-acryloxy propane; 2-hydroxybutyl acrylate; 4-hydroxybutyl acrylate; diethyleneglycol acrylate; 5-hydroxypentyl acrylate; 6-hydroxyhexyl acrylate; triethyleneglycol acrylate; 7-hydroxyheptyl acrylate; 1-hydroxy-2-methacryloxy propane; 2-hydroxypropyl meth-acryloxy propane; 2-hydroxypropyl methacrylate; 2,3-dihydroxypropyl methacrylate; 2-hydroxybutyl methacrylate; 3-hydroxybutyl methacrylate; 2-hydroxyethyl methacrylate; 4-hydroxy butylmethacrylate; 3,4-dihydroxybutyl meth-acrylate; 5-hydroxypentyl methacrylate; and 7-hydroxyheptyl methacrylate. Although one of ordinary skill in the art will recognize that many different hydroxy-substituted alkyl (meth)acrylates including those listed above could be employed, the preferred hydroxy functional monomers for use in the resins are hydroxy substituted alkyl (meth) acrylates having a total of 5 to 7 carbon atoms, i.e. esters of C2 to C3 dihydric alcohols and acrylic or methacrylic acids. Illustrative of particularly suitable hydroxy-substituted alkyl (meth) acrylate monomers are 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxypropyl methacrylate, and 2-hydroxypropyl acrylate.
Among the non-hydroxy substituted alkyl (meth)acrylate monomers which may be employed are alkyl (meth) acrylates (as before, meaning esters of either acrylic or methacrylic acids). Preferred nonhydroxy unsaturated monomers are esters of C1, to C12 monohydric alcohols and acrylic or methacrylic acids, e.g., methyl methacrylate, hexyl acrylate, 2-ethylhexyl acrylate, lauryl methacrylate and the like. Examples of particularly suitable monomers are butyl acrylate, butyl methacrylate and methyl methacrylate.
Additionally, the acrylic copolymer resin may include in their composition other monomers such as acrylic acid and methacrylic acid, monovinyl aromatic hydrocarbons containing from 8 to 12 carbon atoms (including styrene, alpha-methyl styrene, vinyl toluene, t-butyl styrene, chlorostyrene and the like), vinyl chloride, vinylidene chloride, acrylonitrile, and methacrylonitrile.
The acrylic copolymer preferably has a number average molecular weight between about 1000 and 6000, more preferably between about 1500 and 5000. Preferred acrylic polymers will contain at least about 5wt % of the purified glycidyl ester component, preferably about 5-35wt %, based on resin solids.
Acrylic polymers of this type and curable coating or paint formulations prepared therefrom containing an amino crosslinker are disclosed in U.S. Pat. No. 4276212. These polymers are generally polymerized in organic solvent solution using free radical catalysts such as organic peroxides or azobis-isobutyronitrile.
Alkyd resins may be prepared by reacting the purified glycidyl ester with polybasic carboxylic acids or anhydrides thereof Illustrative examples of polybasic carboxylic acids include: terephthalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azeleic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid, tetrahydrophthalic acid, isophthalic acid and dimerized fatty acid of drying oils such as soybean oil. Examples of suitable dicarboxylic acid anhydrides are those of succinc acid, glutaric acid, maleic acid, phthalic acid, tetrahydrophthalic acid and hexahydrophthalic acid as well as Diels-Alder adducts of maleic anhydride with various dienes such as terpenes and cyclopentadiene.
Preferred alkyd resins include those disclosed in U.S. Pat. No. 3275583 and U.S. Pat. No. 3397176.
The purified glycidyl esters may also be used as a reactive diluent in resin systems where the epoxy functionality is caused to react with some functionality present on the resin binder. Such resin systems include polyester resins, polycarbonate resins, epoxy resins and like resins, as well as acrylic and alkyd resins.